Cooling water systems and the associated structures that are submerged in surface waters, fresh water, brackish water and/or salt water provide surfaces for the attachment and accumulation of biological organisms. This accumulation can lead to the formation of organic deposits and serious fouling problems. These fouling problems are wide spread and have been shown to accelerate corrosion of the cooling system and their structures. They have also shown to decrease heat transfer and increase frictional losses. These problems directly affect the cooling system and its performance. Fouling of the cooling system can become so severe that the system may not operate properly or efficiently.
Organic fouling of the system falls into two categories, either micro fouling or macro fouling. Microscopic organisms such as bacteria, fungi and algae cause micro fouling. This would also include their organic by-product deposits. These deposits build on the surface and form a biofilm. This biofilm may also contain inorganic debris, which is intertwined in the deposit. Macro fouling is typically caused by the colonization of larger macro invertebrates, which attach themselves to the structure during the larval state and grow large enough to be seen and felt. Examples would be bivalve mollusks and barnacles. Macro fouling of cooling systems is widespread with over thousands of organisms causing the problems. In salt water/brackish water the primary macro foulers are bivalve mollusks and sometimes barnacles. In fresh water the primary macro foulers are bivalve mollusks, bryozoans and sponges.
Controlling biological fouling of cooling systems can prove difficult. An effective industry method is the use of quaternary ammonium compounds (QACs). These products are registered with the EPA as microbiocides. QACs are cationic surfactants and it is their surface-binding activity that produces antifouling biocidal effects. They are allowed for the use in cooling systems. They have been proven effective at controlling microorganisms, as well as macroorganisms. The QACs are introduced into the cooling water of the systems to control fouling. A major drawback to using these products revolves around their toxicity to other organisms once the water is discharged from the plant. For example, it is known that QACs are actively toxic to fish and other aquatic life. To control the level of QAC in the discharge effluent, bentonite clay slurries (mixture of bentonite clay and water) are used. The slurries are typically mixed off-site and injected at a metered rate into the effluent stream. The bentonite clay reacts with the QAC and reduces its toxicity to an acceptable level in the effluent. In particular, the QACs readily and strongly absorb to clay particles and other negatively charged surfaces. Following absorption, the compounds are degraded by microbes.
A major drawback in using bentonite clay slurries is the large volume of clay slurry, which is needed to effectively detoxify the quaternary ammonium compound. The ratio of clay slurry to quaternary ammonium compound can be up to 80:1 to sufficiently decrease the toxicity level in effluent to within regulatory compliance. This creates a major logistic problem. For example, some applications require over two tank wagons (4,500 gallons each) of clay slurry to properly detox approximately 115 gallons of quaternary ammonium compound. With the clay slurry being mixed off-site, transportation and storage of the large volumes of clay slurry are concerns.
U.S. Pat. No. 4,021,021 ('021) discloses a wetting system for wetting dry powders, such as bentonite clay, with water as part of a clay-polymer water treatment process for producing drinking water. This system includes a wetting tank for receiving water and a continuous flow of fine powder feed. Powder can be fed with variable speed to the tank. Clay powder is dumped onto the surface of the water in the wetting tank where it is mixed to form a clay-water mixture which is continuously withdrawn for transfer to an aging tank to swell before use. The swelled clay-water mixture can be injected into raw water entering a water treatment plant, after which time a suitable polymer can be injected into the water. The water is then directed to a settling tank. The '021 patent does not disclose directly transferring the clay-water mixture from the wetting tank and into an effluent stream. Moreover, this patent does not disclose treating water contaminated with anti-biofouling quaternary amine compounds.